The present invention relates to a test device and determination of a chemical or biochemical component (analyte) in an aqueous body fluid, such as whole blood. In particular the present invention relates to a dry reagent test strip from which an analyte presence and/or concentration is determined by use of an instrument. A common use of such test strips is for determination of glucose level in blood by diabetics.
Numerous devices have been developed to test for presence and quantity of analytes in aqueous samples, such as whole blood or urine. The patent and technical literature of the last thirty years is replete with inventions which utilize a reagent strip containing a dry chemistry reagent system, that is, a system in which the wet chemistries are imbibed into an absorbent or bibulous medium, dried, and later reconstituted by fluid from the test sample. The reagent strips contain an indicator which changes color, depending on the presence or concentration of a particular analyte in a biological fluid applied to the strip. These strips may be read visually by reference to a color standard or colorimetrically by instrument calibrated or programmed to detect a certain color. Although some of these strips use reduction chemistries, more commonly they involve an oxidizable dye or dye couple. Some of the strips include an enzyme, such as glucose oxidase, which is capable of oxidizing glucose to gluconic acid and hydrogen peroxide. They also contain an oxidizable dye and a substance having peroxidative activity, which is capable of selectively catalyzing oxidation of the oxidizable dye in the presence of hydrogen peroxide. (See, for example, U.S. Pat. No. 4,935,346, to Phillips et al.) Examples of these devices, in addition to those used to test blood glucose, include tests for cholesterol, triglycerides, calcium or albumin in whole blood, and for protein, ketones, albumin or glucose in urine.
Dry chemistry reagent strips incorporating enzyme-based compositions are used daily by millions of diabetics to determine blood glucose concentrations. The NIH sponsored study, tire Diabetes Complications and Control Trial, demonstrated conclusively that careful control of blood glucose levels can significantly reduce the incidence of serious complications of diabetes such as vision loss and kidney malfunction. Most diabetics must test themselves periodically in order to make appropriate adjustments to their diet or medication. It is thus especially important for diabetics to have rapid, inexpensive, and accurate reagent strips for glucose determination. The embodiment of dry chemistry reagent systems in test strips enable simple yet effective analytical protocols.
The technologies embodied in the products which have been developed to date have certain limitations from the perspective of the end user and/or the manufacturer. Colorimetric strips that dose on the meter can lead to contamination of the meter. Further, many patients with arthritis or vision impairment have difficulty bring a drop of blood which is hanging on one of their fingers to a small application spot on the strip in the meter. Dosing off the meter, placing the sample on the strip and then inserting it into the meter, also can still lead to contamination. Electrochemical strips deal with the contamination issues, but the manufacturing difficulties and cost can be prohibitive.
There is, therefore, a need to overcome some of the limitations of currently available testing systems. U.S. Pat. No. 3,092,465, issued to Adams et al., U.S. Pat. No. 3,298,789, issued to Mast and U.S. Pat. No. 3,630,957, issued to Rey et al., all describe a basic reagent system which became a standard for colorimetric determination of glucose in biological samples. These patents describe the formation of a film layer or semi-permeable coating over the bibulous matrix to hold back the larger particulates, such as red blood cells, and allow fluid to permeate into the bibulous matrix. This approach requires the removal of red blood cells by washing or wiping to enable visual inspection or instrument reading of the indication of the dye color formed in the matrix.
Stone, U.S. Pat. No. 3,607,093, discloses a membrane for testing blood where the membrane has a skin permeable to solutions but impermeable to solids such as red blood cells and to macromolecules such as proteins. This membrane is disclosed as being used by applying a blood sample then wiping away the red blood cells from the skin in order to reach the test indication through the skin.
U.S. Pat. No. 3,552,928, issued to Fetter discloses the use of certain water soluble salts and amino acids in reagent formulations as separation agents to provide blood separation. With solids such as red blood cells substantially removed from the biological fluid, there is less background color at the test site to obscure a change in coloration produced by a testing reagent.
Phillips et al., U.S. Pat. No. 4,935,346 discloses a system wherein a whole blood sample is applied to the device and indicator development occurs in the presence of the colored components of the sample. Measurements of the color change in indicator are made at two distinct wavelengths to eliminate the interferences from the presence of colored blood components.
Terminello et al., U.S. Pat. No. 4,774,192, disclose a system in which the matrix is formed of an asymmetric material used to filter the red blood cells in the sample. The asymmetric material has a density gradient from one side to the other to progressively separate red blood cells from the fluids.
Daffern et al., U.S. Pat. No. 4,994,238, disclose a test device that comprises an asymmetric reagent layer that has progressively finer filtration with increased distance from one surface toward the other surface.
Castino et al., U.S. Pat. No. 5,456,835 disclose the use of filters formed of ligand modified polymeric film such as polypropylene fibers and polyethersulfone fibers.
Vogel et. al., U.S. Pat. No. 4,477,575, disclose the use of glass fiber material to achieve blood separation through the thickness of the material. Blood is applied to one side of the glass fiber, and relatively clear fluid migrates out of the opposite side. This fluid is delivered to an additional layer where the detection of analytes can occur.
Macho et al., U.S. Pat. No. 5,451,350, disclose the use of absorbent channels to distribute sample fluid in multi-zone test devices. Charlton et al., U.S. Pat. No. 5,208,163, also disclose the use of capillary channels to distribute blood to various chambers in the device.
The disclosures of the above patents are incorporated herein by reference.
The prior art devices and methods of the above references provide varying degrees of effectiveness of blood analysis at varying degrees of complexity and cost.
It is an object of the present invention to provide enhanced devices and methods to improve the performance and minimize the cost and complexity compared to the prior art devices.
It is another object of this invention to provide a capillary format for testing which is easy to sample and dose and to manufacture.
It is another object of this invention to provide a configuration or format for testing which permits the patient to use xe2x80x9cnon traditionalxe2x80x9d body locations, other than the fingertips to extract a sample of body fluids.
It is another object of this invention to provide a means for performing microtitration by limiting the volume of a bodily fluid used to perform the analysis.
It is another object of this invention to provide a means for delivering a measured volume of a bodily fluid to the test area.
It is still a further object of this invention to provide a dry chemistry reagent test strip which can be used in or read by an electronic meter to analyze body fluids for one or more analytes.
The above objects as well as others are achieved by the devices, methods and systems of this invention as disclosed herein.
In one aspect this invention provides a method of testing body fluids for the presence or concentration of an analyte by using a porous matrix. Pending U.S. patent application Ser. No. 08/628,489 filed Apr. 5, 1996 describes the use of microporous matrix material and the concept of microtitration which are well suited for use in this invention, the disclosure of which application is incorporated herein by reference.
In another aspect this invention provides a device that contains body fluids during testing that eliminates the problems of meter contamination, and it""s simple colorimetric design greatly reduces the difficulties of manufacturing and cost.
In a preferred embodiment of the invention the device consists of a capillary system which is used to collect the sample of body fluid and deposit it onto a reagent membrane for analysis. The use of a capillary tube to collect the sample permits the patient to collect a sample from a non finger tip location thereby increasing the number of possible sampling sites from which to extract a sample of body fluid. The apparatus comprises of a hydrophilic capillary tube in communication with a hydrophilic capillary wicking or spreading material which is in communication with an absorbent reagent membrane. The reagent membrane has been imbibed with indicator reagent system capable of indicating the presence or concentration of the analyte.
In another aspect, this invention uses the concept of microtitration to limit the volume of the sample thereby improving the accuracy of the test. The capillary wick and/or the membrane is bounded to the injection molded capillary and handle thereby creating a defined volume for the absorption of the sample. The user applies a blood sample to the capillary by placing the capillary tube in communication with the sample and allowing it to wick up the tube and wet out the membrane. The fluid passes through the capillary spreading layer/filter onto the membrane. The reading or measuring for the presence/concentration of the analyte being tested is accomplished by detecting the change in reflectance of the reagents which are imbibed into the membrane. The embodiments of the devices of the invention with the appropriate dry chemistry system in the matrix member can be used in test strips which may be read or measured in an electronic meter.
In another aspect, this invention provides a strip for testing for the presence or concentration of an analyte in a fluid comprising a support member; a spreading layer on the first side of the support member; a reagent layer on the spreading layer which comprises a reagent selected for the analyte of interest; and a capillary tube on the opposite side of the support member communicating through an aperture in the support member with the spreading layer, whereby a fluid containing an analyte introduced into the tube flows through the tube and the spreading layer to contact the reagent. Optionally the strip can further comprise a carrier layer on the reagent layer and positioned on the other side of the reagent layer from the spreading layer and an aperture in the carrier layer for observing or measuring the indication of the reagent.
In another aspect, this invention provides a method of testing a fluid for the presence or concentration of an analyte comprising providing a test strip comprising a support member; a spreading layer on the first side of the support member; a reagent layer on the spreading layer which comprises a reagent selected for the analyte of interest; and a capillary tube on the opposite side of the support member communicating through an aperture in the support member with the spreading layer, whereby a fluid containing an analyte introduced into the tube flows through the tube and the spreading layer to contact the reagent; introducing sufficient fluid containing an analyte into the capillary tube to flow onto the reagent layer; and observing or measuring the indication of the reagent.
In another aspect, this invention provides a method of making a strip for testing for the presence or concentration of an analyte in a fluid comprising: providing a support member with a capillary tube positioned on one side of the support member and communicating with the opposite side of the support member through an aperture in the support member; mounting a spreading layer on the opposite side of the support member and in communication with the aperture in the support member; and mounting a reagent layer on the spreading layer. Optionally the method includes a method comprising: mounting a carrier strip on the reagent layer opposite the spreading layer; and providing an aperture in the carrier layer for observing or measuring the indication of the reagent. Preferably, the method includes preassembling the carrier layer, the reagent layer and the spreading layer; and mounting the preassembled layer on the support member.
The above sets forth the generic aspects of the device and methods of the present invention. These device and methods are more fully described in the drawings and the descriptions below.